The main rule of thumb when deciding on a topic is to choose a topic that interests you. Your lecturers may be able to advise you in this regard; your supervisor certainly will. It is also worth spending time in the library browsing journals in your area for information and inspiration on up-to-date topics. The chart below will help set some parameters for you:
(Kelly, 2014)
Brainstorming is a great way of coming up with a range of keywords for your topic. Keep a list of all the keywords you come up with.
This list will drive your database searches, and help you to find lots of useful information on your topic.
(Waterloo Library, 2013)
When you start searching the library databases, you may realise that you need to tweak your topic in order to find relevant information, that is not too broad or too narrow. Be flexible with your keywords and be prepared to re-focus your topic. Refer back to the list of keywords you created in the Brainstorming phase above, and add more options for searching. This is all part of The Research Process, as outlined below:
(Bogan, 2014)
(NC State University Libraries, 2013)
The Library, Technological University of the Shannon